1. Due to the chemical reaction between the
solder flux and the alloy surface, different fluxes should be selected for different alloy components; due to the poor wettability of lead-free alloys, high flux activity is required; the activation temperature of flux should be increased to adapt to lead-free high temperature Soldering temperature ;) Less post-soldering residue, and non-corrosive, meeting ICT probe capability and electromigration.
2. The key to solder paste printability and solderability lies in flux. Once the lead-free alloy has been identified, the key is the flux. Select the solder paste to do a process test to see if the printability can meet the requirements and the quality after soldering. In short, choose the solder paste that suits your product and process.
3. Lead-free solder must be specially prepared. Flux in solder paste is a key material to purify the soldering surface, improve wettability, prevent solder oxidation and ensure the quality of solder paste and excellent manufacturability. At high temperature, the flux cleans the oxide layer on the PCB pad, component terminals and pin surface, and activates the metal surface at the same time.
4. The VOC-free no-cleaning soldering flux in wave soldering also needs special preparation. Lead-free solder pastes and water-soluble fluxes for wave soldering are also required for some products.
Adverse effects of high temperature on components:
Ceramic resistors and special capacitors are very sensitive to the slope of the temperature curve (temperature change rate). Due to the large difference between the thermal expansion coefficient CTE of the ceramic body and the PCB, it is easy to cause cracks in the component body and solder joints when the solder joints are cooled. The difference in CTE is directly proportional to the temperature and the size of the component. Aluminum electrolytic capacitors are extremely sensitive to sharpness: connectors and other plastic packaged components fail significantly at high temperatures. The solution is to reduce the peak temperature as much as possible; to dehumidify and bake the moisture-sensitive components.
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